Method of treating carbonates



Feb. 1, 1938. P. MccoMB METHOD OF TREATING CARBONATES Filed Sept. 4,1934 Parker M 60/77 5,

Patented Feb. 1, 1938 UNITED STATES PATENT OFFICE 1 Claim.

This invention relates to the reduction of minerals and ores to oxidesand by-product gases.

It is an object of my invention to provide a roasting oven which willroast stone or ores without permitting the stone, at any place in itstravel through the oven, to come into direct contact with the productsof combustion.

A further object of this invention is to provide a roasting oven with avertical type roasting chamber in which the material being roasted maybe lowered as a unit.

Another object of this invention is the provision of a roasting ovenhaving a hopper located in the path of the products of combustionwhereby to dry the charge.

Another object of this invention is to provide an improved process ofburning stone, ore or the like, and to separate the resulting by-productgases by allowing them to stratify according to their various specificgravities.

Other objects and advantages of my invention will be apparent during thecourse of the following description.

In the accompanying drawing forming a part of this application, and inwhich like numerals are employed to designate like parts throughout thesame,

Fig. l is an elevation view in part section of a roasting oven embodyingmy invention,

Fig. 2 is a cross sectional view of the same on line 22 of Fig. 1,

Fig. 3 is a cross sectional view of the same on line 33 of Fig. 1,

Fig. 4 is a cross sectional view of the same on line 4-4 of Fig. 1,

Fig. 5 is a cross sectional view on line 5-5 of Fig. 1, showing detailsof a valve feature of this invention.

In the drawing wherein, for the purposes of illustration, is shown apreferred embodiment of this invention, numeral I designates thefoundation of the same. The foundation is fabricated from structuralsteel or other suitable building materials and is designed to hold upthe oven to a suificient height to permit dump carts or other typeconveyors to be passed under the oven to receive the finished product.The outer wall, forming the stack 2 of this oven, is constructed of firebrick throughout its entire length. However, other types of material maybe substituted for fire brick toward the top of this oven where the heatis less intense. From the foundation l, upwardly to line :1:a:, thestack 2 of this oven is made in the form of a hollow rectangular prism.From line :c-r upward to the top of the stack, it is formed in the shapeof a hollow cylinder.

Located inside the stack 2, there is a roasting chamber 3, which isuniformly rectangular in cross sections throughout its entire length.This chamber is anchored along its narrow faces to the stack 2 frompoints 4 down to the bottom of the stack 2. From the bottom of the stack2 to points 4, gas spaces are provided between the wide faces of theroasting chamber 3, and stack 2. To prevent any distortion of theroasting chamber which might result from the condition of highcombustion temperatures, it has been found advisable to anchor theroasting chamber 3 along its narrow faces to the stack 2. From points l,upwardly, with the exception of the area at the discharge manifolds 5,the roasting chamber 3 is spaced from the stack 2 on its narrow faces aswell as its wide faces to permit products of combustion to contact agreater heating surface.

The roasting chamber 3 is to be constructed out of suitable refractorymaterials having a high thermal conductivity value, such as aluminumoxide, beryllium oxide, thorium oxide, silicon carbide, zircon, or frommetals such as tungsten, molybdenum, etc., having high melting points.The roasting oven is preferably constructed by superimposing individualtiles, one on another, and cementing them together.

Numeral 5 designates discharge manifolds. These manifolds are fabricatedfrom the same materials that the roasting chamber 3 is fabricated. Thesemanifolds 5 may be cast as units but are more preferably constructed insome superimposed hollow tile construction followed in the constructionof the roasting chamber 3. Exhaust ports 5 are provided in the narrowwalls of the roasting chamber 3. These ports are slanted upwardly sothat they can not get clogged with stone.

Numeral l designates discharge pipes through which the generated gasesmay be drawn off by means of a pump not shown.

Numeral l0 designates a funnel shaped loading hopper. The loading hopperI0 is supported on the top of the stack 2 by means of a frame I I. Theloading hopper l0 terminates at its lower end in a rectangular spout I2,which is made smaller than the mouth of the roasting chamber 3, intowhich it extends to provide a clearance space through which waste gasesmay be floated ofi.

As the temperatures at this part of this oven are not extreme, I makethe loading hopper l out of metal of high thermal conductivity values.

The apron HI of the loading hopper It may be provided with ports Hlopening upward and outward so as to allow escape of waste gases from theraw material as it is being dried and heated.

The furnace structure proper of the stack consists in the rectangularbrick work of the stack 2 from its floor up to line x--.r, and isdesignated by numeral l3. Through holes I4 in the opposite narrow wallsof the furnace I3, are mounted burners 15. These burners are mounted,preferably, in such a position thatthe flames coming from them strikethe roasting chamber 3 at right angles on its broad faces. While most ofthe combustion takes place in the furnace l3, it is true that, undersome conditions, some of the combustion takes place at points higher upin the stack 2. To insure complete combustion, adjustable dampers l6(see Fig. are provided in the floor of the furnace l3 to admit excessair when needed. It has been found advantageous to carry the burner feedlines l1, both fuel and air, through the furnace so that both the airand fuel may be preheated for the sake of economy and for the sake ofproducing higher burning temperatures in the burner flames.

Referring to Figs. 5 and 1, numeral I 8 designates a take-off hopper and19 a metering valve mounted at the extreme lower end of the take-offhopper to enclose the same. The metering valve I9 is of a cylindricalshape and is provided with longitudinal pockets 20.

When the metering valve I9 is rotated, the measures of stone that settleinto the pockets are passed out and allowed to fall by gravity into somesuitable container or onto a moving conveyor.

The stack 2 is provided with suitable peep holes 2|, through which thetemperatures of the products of combustion may be observed at thevarious points of its travel.

This oven may be constructed in various sizes,

depending on the volume or materials to be treated, or may beconstructed in a battery of units. It has been found practical that anoven of .this type to ft. in height will provide sufiicient contactsurface for the preheating and the separation of gases, complete burningof the raw material, and also provide a preliminary cooling chamber inthe oven. The burner should be placed at about one-fourth the height ofthe oven, the ports at about two-thirds to threefourths of the height ofthe oven.

Among the ores and minerals that can be burned, roasted, vitrified,disintegrated, reduced or fused in the oven, are: galena, sphalerite,chalcopyrite, chalcocite, pyrites, gypsum, cerrusite, smithsonite,limestone, marble, malachite, azurite, magnesite, dolomite. Theprincipal byproduct gases given off by the above named materials aresulphur dioxide (SOz),'having a specific gravity of approximately 2.2,and carbon dioxide (CO2), having a specific gravity of approximately 1.5as compared with air. The ore or mineral to be treated is first crushedto a size that will permit it to be readily attacked by heat. Generally,a fineness that will pass a one or two inch screen is sufficient.

If the ore or mineral to be treated istobe acted on with a reagent,oxide or silicate, this oxide or silicate or other agent is then mixedwith the stone charge either before or after crushing. r

In operating my oven, the roasting chamber 3 is supplied with stone orthe like from the hopper H]. The roasting chamber 3 should be keptfilled and an extra supply of the stone or the like should be held inthe hopper.

As the flue gases issuing from the stack 2 must, by design, impinge onthe hopper, the portion of the charge in the hopper is heated by thetransfer of the heat from the flue gases to the charge through the metalhopper. The hopper is made out of an efficient heat conducting'metal,whereby, to more effectively use the waste heat of the escaping fluegases.

The valve 20 at the bottom of the take-off;

hopper acts as a closure for it. Through the means of pockets 20 in thesurface of the valve, definite quantities of the burned charge may bemetered out as the, valve is revolved. In this way the entire chargeinthe roasting oven is gently lowered. As the roasting oven 3 is vertical,the force of friction of the roasting ovens walls on the charge will betoo slight to stir up the charge, with the consequence that the entirecharge in the roasting chamber 3 may be lowered as a unit.

The heat necessary to reduce the charge to oxides and the by-productgases, S02, CO2, etc., is supplied by burning fuel through means ofburners I5. Gas or oil are excellent fuels to use in this oven becausethe combustion of these against the opposite broad faces of the roasting'35 chamber 3. This is the hottest point in the oven. The fuel and airsupplies, as previously explained, are preheated to effect a highertemperature than would ordinarily occur from the burning of a mixture ofcold fuel and air, since the heat 1 requisite to bring themixture up tothe flash point has been already partly supplied to the fuel and airthemselves separately.

To insure complete combustion, excess air'is admitted through the floorof the furnace to the 1 stack 2 by means of dampers I6. An occasionalbaffle member 2 may be extended inwardly from the stacks inner Wall intothe flue tocreate eddies and prevent the flue gas from channelling andpassing out without giving up its heat.

The temperature in the furnace portion l3 of the stack 2' and the otherportions of the stack and the resulting temperature in the roastingchamber 3 itself will depend on' the material being treated and thelength of time such material remains in the oven. 7

For example, the temperature range necessary to reduce normal carbonatesinside the roasting chamber 3 proper would have to be'from 1200 F. to3000 F. to produce metallic oxides and C02.

The temperature of the flue gases leaving the stack should be maintainedat about 200 'F'.

At no place in the stack 2 are the products of combustion allowed tocome in direct contact with the charge itself. All of the heat that thecharge in the roasting oven 3 receives from the combustion of the fuelhas to pass through the walls of the roasting chamber 3. This feature ofour invention is very important since it insures againstanycontamination of the charge from the fuel. 7

From the drying zone A, where the charge is dried in the hopper by thees caping flue gases, the charge passes into a preheating zone B at thetop of the roasting chamber. In-zone'B 18.3575

charge is being heated both by the heat from the flue gases and also byascending gases which have been generated lower down in the roastingoven 3. In the preheating zone B, exhaust ports 6 provide communicationbetween the roasting oven 3 and the discharge manifolds 5, provided withdischarge pipes 1, whereby the gases generated in the roasting oven 3may be drawn ofi.

In the generation of S02 or CO2, which have greater specific gravitiesthan air moisture and the other gas impurities, the flow from theexhaust pipes may be so restricted as to build up the level of thecolumn of S02 or CO2 with a resulting increase in pressure to such anextent that the gas impurities, and even a part of the $02 or CO2 may befloated up and out of the roasting chamber 3. Since the CO2 gas which isgenerated at the bottom portion of the vertical retort is heavier thanthe air and moisture in the portion of the charge at the top portion ofthe retort the volume of CO2 gas and volume of air and moisture willremain separated along a natural level in the absence of any stirringaction. To assure that there will be no stirring action during thecarrying out of this process the charge of ore that is being heated islowered as an undisturbed unit. That is to say the individual lumps ofore in the charge stay in their same relative position with respect toone another during their entire travel through the oven. This type ofoperation of our oven will insure the production of a very pure gas. Asthe charge is lowered past the exhaust ports 5, any generated gas whichwas trapped in the voids of the charge may be drawn off along with theascending stream of generated gas.

After the charge has passed down through the preheating zone B, itenters into the reducing zone C in the oven, where the charge in theroasting chamber 3 is burned, fused, vitrified or otherwise reduced.

When a charge of normal carbonates is used, it will be completelyreduced in this zone to its metallic oxides and. CO2.

In leaving the reducing zone C, the charge passes through the coolingzone D, preparatory to entering the take-off hopper l8. In cooling, thecharge gives up part of its heat to the incoming fuel and air beingbrought to the burners.

From the cooling zone D the charge, now the finished product, enters thetake-01f hopper I8, which, as previously explained, is closed at itsbottom by a metering valve l9.

The metering valve 19 is intended to be rotated by a gear or like meansand its speed to be controlled by a suitable control means so that thedown flow of the charge may be uniformly controlled.

When the temperature of the burners is held constant, the entireregulation of the furnace resolves upon the regulation of time underwhich the charge is subject to the constant temperature. The timeelement is determined by the rate of flow of the charge which is in turnregulated by the metering valve [9. And so I say that, with a constanttemperature maintained, the degree to which the charge is burned may becontrolled by regulating the meter valve l9.

To insure the purity of the by-product gases, care must be taken whendrawing off the byproduct gases to maintain sufiicient pressure in thepreheating zone B at the ports 5, so that no down draft is created in orthrough the top portion of preheating zone B above ports 5 and tomaintain a proper separation zone between the generated by-product gasand the gas impurities.

It is to be understood that the form of my invention shown and describedis to be taken as only a preferred embodiment of the same, and thatvarious changes in size, shape and arrangement of parts may be resortedto without departing from the spirit of my invention or the scope of thesubjoined claim.

Having thus described my invention, I claim:

The method of treating carbonates, comprising applying heated productsof combustion to the exterior of a vertical retort having its upper endopen and in free communication with the atmosphere so that the heatapplied to the retort decreases upwardly for afiording a lower reducingzone and an intermediate pre-heating zone and an upper drying zone,introducing a loose charge of a carbonate comprising aggregates whichare approximately one-inch to twoinches in size and having voids betweenthem into the upper open end of the retort and gradually moving thecharge downwardly through the retort so that it is subjected insuccession to the action of heat in the drying and pre-heating andreducing zones, discharging the gases from the charge in the drying zoneupwardly through the open end of the retort, preventing any substantialamount of gases other than carbon dioxide gas from entering thepre-heating zone by causing a portion of the carbon dioxide present inthe pre-heating zone to pass upwardly through the voids in the charge inthe preheating zone and drying zone and thereby forcing other gasesthrough the voids in the drying zone and finally discharging to theatmosphere through the upper open end of the retort, and withdrawing aportion of the carbon dioxide from the pre-heating zone.

PARKER McCOMB.

